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Greenhouse Gas Emissions

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What about Greenhouse Gas Emissions?

Greenhouse gases (GHGs) trap heat within the earth's atmosphere. Although most GHGs occur naturally and help keep the earth hospitable to life, they are also generated by human activities. CO2 emissions account for more than 80 percent of the U.S. GHG emissions. These emissions are contributing to changes in the planet'sclimate that could lead to harmful effects, such as sea-level rise and changes in global hydrological patterns. Although the United States makes up 4.4 percent of the world'spopulation, it emits about 16 percent of carbon emissions from fossil fuel combustion.

Sources of Greenhouse Gases (2013)

Title: Pie chart showing the percentage contribution to greenhouse gas emissions by source in the United States in 2013 - Description: The pie chart shows the estimated contributions to greenhouse gas emissions by source in 2013. Transportation contributes 27%, industrial sources contribute 21%, commercial and residential uses account for 12%, agriculture contributes 9%, and electricity generation and use contributes 31%.

Source: U.S. Environmental Protection Agency, U.S. Greenhouse Gas Inventory Report: 1990-2013, https://www3.epa.gov/climatechange/ghgemissions/usinventoryreport.html

Greenhouse gas emissions from transportation primarily come from burning fossil fuel for our cars, trucks, ships, trains, and planes. Overall, transportation contributes 27 percent of national GHG emissions.

Source: Boden, T.A., Marland, G., and Andres, R.J. (2015). National CO2 Emissions from Fossil-Fuel Burning, Cement Manufacture, and Gas Flaring: 1751-2011, Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, doi 10.3334/CDIAC/00001_V2015. http://cdiac.ornl.gov/trends/emis/tre_coun.html

In contrast to most criteria pollutants, emissions of GHGs have been rising from most sectors. From 1990 to 2013, carbon emissions from transportation grew by 16 percent.

Change in Carbon Emissions (1990–2013)

Title: Line chart showing the change in carbon emissions for six sectors in billion metric tons of carbon from 1990 to 2013 - Description: The line chart shows the change in billions metric tons of carbon between 1990 and 2013 for six sectors. The Electricity line begins at approximately 1.9 in 1990, climbs steadily to just under 2.5 by 2007, and drops to just above 2.0 by 2013. The Transportation line begins just above 1.5 in 1990, climbs steadily to 2.0 by 2007, and drops to about 1.8 by 2013. The Industry line begins at approximately 1.6 in 1990, remains relatively flat through 1997, drops slowly to 1.5 by 2007, dips to about 1.3 in 2008, and then slowly climbs back to about 1.4 in 2013. The Agriculture line begins at 0.5 in 1990 and climbs very slowly to a little above 0.5 by 2013. The Commercial line begins just under 0.5 in 1990 and remains basically flat throughout all years. The Residential line begins slightly under the Commercial line and remains relatively flat throughout all years.

Source: U.S. Environmental Protection Agency, U.S. Greenhouse Gas Inventory Report: 1990-2013, https://www3.epa.gov/climatechange/Downloads/ghgemissions/US-GHG-Inventory-2015-Main-Text.pdf

Highway vehicles are the largest users of transportation energy, accounting for 82 percent of the total.

Transportation Energy Use by Mode (2012)

Title: Pie chart showing energy use by transportation mode by percentage in 2012 - Description: The pie chart shows the estimated energy use by the various modes in the transportation sector in 2012. Highway vehicles account for 82%, rail is 2%, waterborne activity uses 4%, air transportation is 9%, and pipeline use is 3%.

Source: U.S. Energy Information Administration, Annual Energy Outlook 2015, Table A7–Transportation Sector Key Indicators and Delivered Energy Consumption, April 2015, http://www.eia.gov/forecasts/aeo/data/browser/.

The amount of energy used and its intensity is an indicator for the amount of GHGs produced. Per passenger mile, transit and passenger rail commuter transportation modes are less energy intense than light-duty passenger vehicles. However, light-duty trucks are more energy intense. For freight transport, heavy-duty trucks are considerably more energy intense than rail on a ton-mile basis.

Transportation Energy Intensity (2012)

Title: Bar graph showing the estimated intensity of energy use in transportation in British thermal units (BTUs) in 2012 - Description: The bar graph compares the intensity of energy use between certain modes and vehicle types. Passenger vehicles, light duty trucks, transit buses, Amtrak rail, and airplanes are measured by the amount of BTUs per passenger mile. Freight rail is measured by BTUs per freight car mile. Heavy duty trucks are measured by BTUs per vehicle mile. The graph shows that transit, air, and passenger rail commuter transportation modes are less energy intense than light-duty passenger vehicles. For freight transport, heavy-duty trucks are considerably more energy intense than freight rail, 22,000 BTUs versus 14,000, while both are significantly more energy intense than the other four modes (2,000-5,500 BTUs).

Source: Bureau of Transportation Statistics, National Transportation Statistics, Table 4-20, 4-25: Energy Intensity of Passenger Modes, April 2015,

http://www.rita.dot.gov/bts/sites/rita.dot.gov.bts/files/publications/national_transportation_statistics/html/table_04_20.html

http://www.rita.dot.gov/bts/sites/rita.dot.gov.bts/files/publications/national_transportation_statistics/index.html

Transportation Energy Data Book: Edition 33, ORNL-6990, Oak Ridge National Laboratory, July 2014, http://cta.ornl.gov/data/tedb34/Spreadsheets/Table2_17.xls

Updated: 5/4/2016
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